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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



This output voltage varies with the position of the armature which serves 

 as one plate of an air capacitor controlling the frequency of an oscillator. 

 The voltage across a coupling impedance in the plate circuit of the os- 

 cillator is rectified to provide the output voltage of the gauge. 



The gauge Avhich is shown schematically on Fig. 3 may be divided 

 functionally into three main parts: (1) An oscillator which operates in 

 the region of 100 megacycles; (2) A detector sensitive to the frequency 

 of the oscillator and consequently also sensitive to the position of the 

 armature; and (3) A "zero set" cathode follower which connects the de- 

 tector output to the input of a dc amplifier. The dc amplifier has suffi- 



SCANNING 

 CIRCUIT 



OSCILLOSCOPE 



OY XO- 



E7OC 



dx 

 dt 



Evocx 



ELECTRO- 

 STATIC 

 GUAGE 



BLANKING 

 CIRCUIT 



CONTACT OPEN-, 

 CONTACT CLOSED 



_^->-' GAUGE TOLERANCES 



-rE7=0 



P'ig. 1 — Schematic diagram of electronic relay tester. 



